Indigo

Indigo is a term used for a number of hues in the region of blue. The word comes from the ancient dye of the same name. The term can refer to the color of the dye, various colors of fabric dyed with indigo dye, a spectral color, one of the seven colors of the rainbow as described by Sir Isaac Newton, or a region on the color wheel. It can include various shades of blue, ultramarine, and green-blue. Since the web era, the term has also been used for various purple and violet hues identified as "indigo," based on use of the term in HTML web page specifications. The word itself comes from the Latin word indicum, meaning "Indian," because the natural dye was originally exported to Europe from India.

The Early Modern English word indigo referred to the dye, not to the color itself, and indigo is not traditionally part of the basic color-naming system. The first known recorded use of indigo as a color name in English was in 1289. Because enslaved West Africans had extensive knowledge of growing indigo, it became a major cash crop in the American colonies.

Newton regarded indigo as a color in the visible spectrum and as one of the seven colors of the rainbow, placed between blue and violet. Sources differ on its actual position in the electromagnetic spectrum. Some later scientists have concluded that what Newton called "blue" is what is now called cyan, or blue-green, and that what he called "indigo" is what is now called blue. Other scholars reject this idea.

In the 1980s, programmers produced a somewhat arbitrary list of color names for the X Window computer operating system. This led to the HTML and CSS specifications issued in the 1990s using the term "indigo" for a dark purple hue. Since that time, violet and purple hues have also been associated with the term.

Pinpointing indigo to a specific hue value is difficult. Because of the Abney effect, a higher saturation value on the HSV color wheel shifts the hue toward blue. However, on the new CIECAM16 standard, hue values around 290° may be thought of as indigo, depending on the observer.

History

Indigo dye is a blue color that comes from several kinds of plants. The best-known is the indigo plant (Indigofera tinctoria), often called "true indigo." Long ago, people grew these plants in places such as East Asia, Egypt, India, Bangladesh and Peru. The earliest direct evidence of indigo use comes from Huaca Prieta in Peru, dating to around 4000 BC. In early Europe, the main source was the woad plant (Isatis tinctoria). Later, "true indigo" replaced woad as trade routes opened up. Today, plant sources have been largely replaced by synthetic dyes. Spanish explorers found an American kind of indigo and began growing it in Guatemala.

Indigo also came to North America, where Eliza Lucas is credited with introducing the plant to the southern colonies. However, enslaved West Africans were the ones who actually grew the seeds and made the dye. Before the Revolutionary War, indigo made up more than one-third of the value of exports from the American colonies. Later, Newton named indigo as one of the seven colors of the rainbow after shining sunlight through a prism. Scientists still discuss exactly what Newton meant by the name. Today, modern scientists place indigo between blue and violet.

Shades and variations

Like many other colors (orange, rose, and violet are the best-known), indigo gets its name from something in nature: the plant indigo, which was once used to dye cloth (see also Indigo dye). Indigo dye is a greenish dark blue made from the leaves of the tropical Indigofera plant, from woad (Isatis tinctoria), or from Chinese indigo (Persicaria tinctoria). Cloth is boiled in the dye again and again, and each time it becomes a darker blue. The Cherokee Indians rubbed tallow on their hands while working with the dye, and in Sa Pa, Vietnam, the leaves are soaked until the water turns blue, then pickling lime is added. Cloth made from hemp is then dipped in the dye. The pigment indigo matches the web color indigo, and a vat of dye looks closer to midnight blue. The word "indigo" has also been used for several hues since HTML color names were adopted during the World Wide Web era.

Indigo can describe several shades. "Electric indigo" is a bright, saturated color between traditional indigo and violet, and it is the brightest indigo a computer screen can show. In an RGB color space, indigo is mostly blue with some red and no green. In a CMYK color space, it is made from cyan and magenta, with no yellow or black. On a color wheel, indigo can be made by mixing violet with blue, and a nearly identical color is electric ultramarine. Electric indigo sits near the middle of the part of the rainbow traditionally called indigo, though actual spectral colors fall outside the gamut of the sRGB system (see CIE chromaticity diagram). Web color "blue-violet," also called "deep indigo," falls between electric indigo and pigment indigo in brightness. The web color indigo is closer to violet than to the indigo dye it is named after (see § Web era). A "web-safe indigo" is similar to the color wheel indigo but less intense. "Tropical indigo," called añil in a 2005 color guide by Rosa Gallego and Juan Carlos Sanz, is widely popular in the Hispanophone world.

In nature

Male indigobirds are a very dark, metallic blue. The indigo bunting, native to North America, is mostly bright cerulean blue with an indigo head. The related blue grosbeak is, ironically, more indigo than the indigo bunting.

Lactarius indigo is one of the very few mushrooms colored in tones of blue. The eastern indigo snake, Drymarchon couperi, of the southeastern United States, is a dark blue/black.

In culture

Indigo shows up in many parts of everyday life. IndiGo is an Indian budget airline that uses an indigo logo and flies only Airbus A320s. Indigo Books and Music also uses an indigo logo, and the GameCube was first released in two color versions, one called 'Indigo'. In computer graphics lighting, electric indigo is sometimes used as a glow color, possibly because it seems to change to lavender when mixed with white. In 2008, scientists found that a ripe banana glows bright indigo under a black light. Some insects and birds can see into the ultraviolet because they are tetrachromats, and they can use this glow to tell when a banana is ready to eat. The glow comes from a chemical made as the green chlorophyll in the peel breaks down. In Marina Warner's novel Indigo (1992), a retelling of Shakespeare's The Tempest, Sycorax produces indigo dye. The French Army adopted dark blue indigo at the time of the French Revolution, replacing the white uniforms of the Royal infantry. In 1806, Napoleon decided to bring back white coats because of shortages of indigo dye caused by the British continental blockade. The blue was kept, however, and indigo remained the main color of French military coats until 1914.

Indigo also has a place in spiritual life. In West and Central Africa, indigo has been grown for thousands of years and plays an important role in the traditional beliefs of the Bamileke, Yoruba, Baoulé, Dogon, Fon, and Aja peoples. The spiritualist movement uses electric indigo, which sits between blue and violet on the spectrum. In New Age philosophy, electric indigo stands for the sixth chakra (called Ajna), which is said to include the third eye and is linked to intuition and gnosis (spiritual knowledge). Alice A. Bailey used indigo as the "second ray," representing "Love-Wisdom," in her Seven Rays system, which sorts people into seven metaphysical psychological types. Psychics often link indigo paranormal auras with an interest in religion or intense spirituality and intuition. Indigo children are said to have mostly indigo auras, and people with indigo auras are said to prefer jobs such as computer analyst, animal caretaker, and counselor. In Wicca, indigo represents emotion, fluidity, insight, and expressiveness, and it is used for spiritual healing.

Dyes

Indigo dye was used to color denim, giving the original 'blue jeans' their distinctive colour. In 1778, Guatemala was considered one of the world's leading providers of indigo. In Mexico, indigo is known as añil, and after silver and cochineal, which makes red, añil was the most important product exported by historical Mexico. In the Philippines, the dye is still used in some places.